In micro-probe microscopy, such as atomic force microscopy (AFM), scanning tunneling microscopy (STM), beam electron emission microscopy (BEEM), and similar technologies, as well as field emission, all hereinafter designated as "micro-probe microscopy" or "MPM", high aspect ratio tips, with extremely sharp ends, are found to be highly desirable. These sharply pointed structures are used to probe atomic or sub-atomic forces associated with surfaces, sometimes forming images of the surfaces. It has been found in the past that silicon tips, formed by various processes of micromachining, are capable of providing the desired aspect ratios with sharp ends.
However, many such tips have been found to be relatively fragile, and in addition, they tend to stick to many species of materials of interest. Etched silicon tips are known to be oxidized very rapidly in air, and to be covered with a slowly increasing layer of oxide, consisting mostly of silicon monoxide. This substance is hygroscopic, and may be the basis for the increased sticking observed in these points, as compared say to pyramidal tips made of silicon nitride.
Others have recognized the value of harder tips. U.S. Pat. No. 4,968,585 to T. R. Albrecht et al. describes tips using Si.sub.3 N.sub.4 and Al.sub.2 O.sub.3. These tips are made by semiconductor manufacturing processes involving deposition of a film, such as Si.sub.3 N.sub.4 on a Si surface. A pyramidal pit is etched as a mold before the film is applied and the film is patterned into a cantilever shape. A glass plate is bonded to the film as a support so that the Si can be etched away leaving the plate supporting the structure. The structure is coated with metal for support and then the glass is removed. If the Si layer had been left in place, the radius of the tip would have increased.
An object of our invention was to devise a method of manufacturing tips for MPM which yields tips with desired surface properties but which does not require multiple layering processes with dissimilar materials. Such a method would be simpler and could lead to sharp tips with superior properties.